The Sweet Grass plate. Relief from Copernicus GLO-30; rivers and lakes from USGS NHD; watersheds from the USGS Watershed Boundary Dataset; roads and city limits from Census TIGER 2024.
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Sweet Grass’s center stands about 3,550 ft above sea level. Within three miles the land runs from 3,400 ft to 3,690 ft, a difference of 290 ft: rolling country.
Under the town center the state geologic map shows Virgelle Formation (sandstone), from the Late Cretaceous, 72 to 84 million years old.
The section below crosses 3 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 18×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone, siltstone, mudstone. Age: Late Cretaceous, 66 to 84 million years old. About 9 mi of the line.
Sandstone. Age: Late Cretaceous, 72 to 84 million years old. About 3 mi of the line.
Gravel, sand, silt. Age: Pleistocene to Holocene, less than 1.8 million years old. About 0.5 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
Heights from Copernicus GLO-90 (a surface model: it includes buildings and tree canopy); summits from USGS GNIS; rivers from USGS NHDPlus HR; rock from the USGS State Geologic Map Compilation.
